How to overcome external wall insulation problems with multifoil

Fitting external wall insulation to your property is an excellent way of improving thermal efficiency – but it also comes with its challenges. In this article, we look at the various issues, and how they can be remedied using multifoil insulation.

The on-going fight to keep fuel bills low in the face of rising costs has come up with a variety of measures designed to retain heat while keeping out cold and draughts.

Many of us have re-lined our loft spaces, replaced poorly performing windows, fitted draught excluders and even purchased thicker curtains – anything to keep those energy bills down.

Included in these measures is wall insulation and again, a fair number of us might have had some form of this fitted internally, for example cavity wall insulation. Perhaps fewer of us have had insulation fitted externally, yet external wall insulation (EWI) is an excellent option for improving thermal viability, especially in houses built with solid walls (and no cavities).

The usual method of applying EWI is to batten it on, then apply render before finishing with a brick fascia or cladding boards. Of course, this changes the face of the property (which is by no means always a bad thing!) but the benefits in terms of heat conservation are enormous.

However, fitting EWI comes with certain problems, aside from changing the overall look of the property. Chief among these is whether the building can actually cope with what is essentially a very heavy overcoat right round it, especially when it wasn’t originally designed for that.

In the UK, older properties were designed to ‘breathe’ via the use of lime-based mortars, internal fireplaces, air bricks, etc. In this way, such properties allowed water vapour to escape through the walls and up chimneys. But over the years, modernisation of such properties – bricking up fireplaces or capping old chimneys, for example – has reduced ventilation, and the same goes for EWI. If it’s not done with proper planning and care, the reduction of air movement can lock in moisture, eventually causing mould and condensation.

Why Multi Foil Makes the Best Insulation

There are also potential problems around windows and doors. These are major sources of both escaping heat and external draughts. Window and door frames can be narrow, and leaving gaps around them when standard EWI is being applied – insulation boards, for example – can create cold bridges, substantially reducing the building’s thermal efficiency.

Finally, even adding EWI with excellent breathability can be counter-productive if it is covered with an inappropriate render. Old-fashioned though it may be, lime render has much more breathability than the standard cement equivalent, particularly if it’s being applied to older houses. And while we’re on that point, EWI on buildings in a conservation area might well be subject to planning permission, so that’s something else to consider.

With all that in mind, are there solutions? In a word, yes. Multifoil insulation, which is made of thin, reflective film that is interspersed with wadding, is a perfect material for EWI. Our product, SuperFOIL, has outstanding thermal properties combined with a vapour control layer and a radiant barrier. Whereas traditional EWI such as foam boards, mineral wool and spray insulation are somewhat one-dimensional, SuperFOIL is a highly flexible solution.

Why is this? Well, having supplied it as EWI to many properties, we’ve seen how it can save space, time and money, as well as achieving the very best results in terms of breathability and thermal efficiency. Fitting SuperFOIL to external walls doesn’t require specialist tools or excessive measuring. It’s quick and easy to install and can be fixed using a continuous method installation with battens, then finished in a suitably breathable render.

Because it’s light, thin and malleable, SuperFOIL can work with a wide range of housing types, including those with curved walls and awkward spaces. Where traditional ‘board’ style EWI can fail, SuperFOIL works a treat – including around windows and doors where heat loss is most prevalent, as mentioned above. In short, SuperFOIL goes well beyond traditional EWI without sacrificing quality, workmanship or thermal excellence.

SuperFOIL is applied using a simple method. First, it is applied to the battens, generally horizontally, by stapling it into place. It is then trimmed and secured by fixing battens around the perimeter to create an airtight finish. To complete the installation, counter battens are fixed vertically on top of the SuperFOIL to create an air gap. Finally, the external finish is fixed to the battens, making sure that the SuperFOIL isn’t exposed to the elements.

We have worked with a wide range of clients, providing our high-end multifoil solutions to projects large and small, easy and complex. For more information about who we are, what we do and how SuperFOIL works in many situations, contact us here or give us a call on 01636 639900.


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